I decided to try out something new, hoping that it might be useful, so starting with this post I will try to build up a collection of plant profiles with information on the cultivation and possible uses of particular plant species. Only plants that I have personally grown with some success will be included, and I will base care instructions mostly on my own experiences with the plant. To begin with I will probably focus on unusual or exotic garden plants that I think deserve to be grown more frequently but I might branch out to include other categories of plants later on. In any case, the first plant to be featured shall be Opuntia humifusa, a very hardy species of prickly pear cactus.
Origin: As its English name suggests, Opuntia humifusa is native to much of the Eastern United States, though it appears to be relatively rare throughout much of its native range. Being a cactus, it prefers sunny, dry locations with sandy or rocky soil. Some wild specimens may be found, for example, in Point Pelee National Park in southern Ontario, which consists of a narrow sandy peninsula that juts out into Lake Erie.
USDA Hardiness Zone: Zone 4b according to various sources, at least Zone 6a based on my own experience.
Opuntia humifusa flowering in my old garden at my parents' previous home in southeastern Michigan
Size: Due to its creeping habit Opuntia humifusa will hardly exceed 8" (ca. 20cm) in height, but its horizontal spread appears to be virtually unlimited if the plant is happy. The flowers are up to 2" (ca. 5cm) across.
Flowering Time: The sulfur yellow flowers appear in late spring or early summer, depending on the local climate. Plants tend to flower more heavily the older and larger the get and since not all flowers open at the same time a plant that is a few years old may flower for several weeks.
Light Requirements: Opuntia humifusa needs full sunlight, the more the better.
Soil Requirements: Being a succulent adapted to arid conditions, Opuntia humifusa needs well-drained sandy soil. I have been most successful with this plant in a south-facing bed backed by three large specimens of Colorado blue spruce (Picea pungens). Due to the trees, the soil in the bed is mixed with a very large amount of spruce needles in various stages of decomposition which keep it light, well-aerated and well-drained. The needles also act as a light mulch, and I think the relatively dry conditions commonly found close to large spruce, fir, and pine trees also help the cactus flourish.
My first specimen of Opuntia humifusa approximately three years after it had been planted as a small cutting with two segments
Siting in the Garden: Opuntia humifusa needs a warm, sunny spot with well-drained soil. South-facing beds and borders are generally the best site for this plant, and sites protected from excessive rain, such as at the base of a south-facing wall or hedge, are ideal. Due to its low height and spreading habit Opuntia humifusa is very well suited for the front of borders, though due its tiny but very irritating spines it should be planted where it is not likely to be in the way of bare feet, shins, or hands.
Care: Once planted Opuntia humifusa needs very little care. Keep weeds in check around the plant is somewhat important since fast-growing weeds such as grasses can easily overtake the low-lying cactus, especially when it is young. As plants get bigger this becomes less of a problem since their ground-hugging, dense habit tends to suppress weeds. Fertilizing is generally not necessary but the plant benefits from a light cover of spruce or fir boughs during the winter months, especially if hungry wildlife is likely to frequent the garden. Do not be alarmed by the droopy, shrivelled, wrinkled look of the plants from the first frost onward. As long as conditions are not excessively wet, the plant will quickly perk up again in mid-spring, and soon afterwords a new flush of "ears" as well as flower buds begin to form.
Propagation: The easiest way to propagate Opuntia humifusa, as with most prickly pear cacti, is to separate individual segments or "ears" from the plant which are then planted. They should be set deep enough that about a third of the segment is below ground. If these cuttings are taken in the spring or early summer, they may be planted right in the spot where they are supposed to grow. They usually root quickly and will often start sprouting new segments during the same season. Some segments also often fall off during winter or early spring and these may very well be used to propagate extra plants. Opuntia humifusa may also be grown from seed; older specimens often produce quite a large number of small red "prickly pears" which ripen in late summer.
Divisions of my original specimen of Opuntia humifusa in the front yard of my parents' new home in the Detroit suburbs, flowering shortly after being transplanted
Use in the Garden: Opuntia humifusa makes a beautiful, eye-catching ground cover for dry, sunny spots, particularly at the front of beds and borders, in rock gardens, and in planting schemes emphasizing native species. With its low, spreading shape it makes a great choice as informal edging for a sunny border.